In such a keyboard known from U.S. Pat. No. 4,400,593, each symbol of the keyboard has associated with it a plurality of keys which are disposed in a plane, at least two of which serve to actuate respective contact sets of an electric contact array in such a manner that the actuation of the contact sets associated with one symbol will initiate the switching operations which are associated with that symbol. Specifically, a particular symbol of the keyboard is associated with each crossing of the gaps between adjacent rows and columns of keys so that each symbol is associated with four keys which constitute a square array. With the condition stated above that each of the gap crossings is associated with one symbol, each key other than the keys at the edges of the keyboard can be used for key actuations associated with four different symbols.
With a view to a simple design of the means for logically combining the contact sets to be actuated and to a reliable operation of that means, it is desirable in such a keyboard that the contact sets associated with a given symbol be actuated simultaneously and that the design of the key-guiding means and synchronizing means required for this purpose should not be unduly complicated.